This invention relates to a radiation detection apparatus, and particularly to a radiation detection apparatus having an auxiliary internal light source and light transmission paths for self checking the operation of the radiation detector as well as the relative contamination of the transparent window in the housing of the detection apparatus.
U.S. Pat. No. 3,952,196, issued Apr. 20, 1976, and owned by the assignee of the present invention, discloses a device for determining whether the optical surfaces through which radiation must travel from a hazardous area of radiation to a radiation detector are free from radiation absorbing material or radiation blocking material. The device disclosed in the patent includes an enclosure for commonly housing both the auxiliary light source and the radiation detector tube, while isolating the same from each other, preventing radiation transmission within the housing from the light source to the detector. The patent also discloses a radiation path from the light source outwardly from the housing to a reflective surface or surfaces external of the housing, which surfaces reflect at least some of the radiation back to the detector through the same optical surfaces that other external radiation passes. The patent contemplates external reflective surfaces which either form a part of the outside housing structure, or are remotely located therefrom.
The prior art invention provides a self checking feature for radiation detection devices in many applications, but also suffers disadvantages which limit its usefulness in certain other applications. For example, when the radiation detection apparatus is placed in a corrosive atmosphere, such as an atmosphere laden with chemically corrosive vapors, the external reflective surfaces tend to suffer from the corrosive or contaminating effects and degrade their ability for efficient light reflectivity. The degradation of the reflecting surfaces causes false fault indications and/or indication that the radiation detection device is inoperative when in fact it continues to function normally in all respects except its self-checking features.
It is therefore desirable to provide a radiation detection apparatus having a self-contained check circuit for periodically testing the light receiving characteristics of the radiation detection tube, and the light transmissive characteristics of the transparent window of the device, without generating false fault indications in situations where the radiation detection device is functioning normally.
It is also desirable to provide a radiation detection device having self-checking features, wherein the device and its self-checking features are all protected from hostile environments.